The present invention relates to a multi-frequency transmission system for implanted hearing aids of the type including a plurality of excitation electrodes implanted together with a receiving part in user's body; the transmitting part includes an electro-acoustic converter connected to a set of band pass filters for filtering a plurality of frequency bands in audio range, and a plurality of high frequency transmitters whose inputs are coupled to respective band pass filters so as to generate at their outputs an amplitude modulated high frequency carrier signal which is applied to a common transmitting coil. The implanted receiving parts have a single input channel and means for selectively applying the received audio frequency bands to the corresponding excitation electrodes.
It has been known how to electrically excite the inner ear of totally deaf persons whose auditory nerve is still intact, by means of a single excitation electrode or by a multiple electrode system which is inserted into the cochlea. The excitation electrodes are distributed on the latter and excited by a high frequency signal from an external receiver so that the auditory nerve of the patient provides an acoustic impression. The principal problem encountered in such prior art hearing aids is in producing such an excitation of the auditory nerve of the patient which would comply as close as possible with the natural hearing resulting from the acoustic conversion in the inner ear. The plural electrodes each vibrating at a different frequency range must be prevented from creating an overlap in the excitation which would make it impossible for the patient to distinguish the differences in received tones. Another problem encountered in implanted hearing aids is the necessity of a full implantation of the high frequency receiver in the patient's body inasmuch any outlets through the user's skin such as for example openings for the sockets of electrodes or other connecting components would require an artificial opening in the skin which of course would be exposed to the risk of an infection.